The present invention relates to a rotation direction detecting apparatus for detecting the direction of rotation of a motor. For example, the rotation direction detecting apparatus is preferably used for detecting the direction of rotation of a drive motor capable of driving various kinds of disk media to rotate in a CD player, a DVD player, a CD-ROM drive, a CD-R drive or a CD-RW drive.
Apparatus for detecting the direction of rotation or rotational velocity of a motor has been heretofore proposed variously.
For example, the Unexamined Japanese Utility Model Application Publication No. Hei2-12619 discloses a rotary encoder in which the size of a slit in a circular disc rotating in a gap of a photo interrupter is set into at least three kinds of widths. When the slit size is set into at least three kinds of widths as described above, the pulse width detected is elongated gradually at the time of clockwise rotation (normal rotation) and shortened gradually at the time of couterclockwise rotation (reverse rotation). Therefore, this rotary encoder is designed to detect the direction of rotation in accordance with the variation in pulse width (this rotary encoder being referred to as background art 1).
On the other hand, the Unexamined Japanese Patent Application Publication No. Hei4-50771 discloses a velocity detector for detecting information of the direction of rotation of a motor as variation in pulse width. That is, slits are provided in four concentric places of a circular disc mounted on a rotary shaft of a motor. These slits are formed so that one-hand edges of the slits are located in positions obtained by equally dividing the circular disc into four radially from the center of the circular disc. The four slits are formed concentrically and successively clockwise at a 1:2:3:4 length ratio. This velocity detector is designed to detect the direction of rotation in accordance with the variation in pulse width because the pulse width is elongated gradually at the time of normal rotation at a constant velocity and shortened gradually at the time of reverse rotation at a constant velocity (this velocity detector being referred to as background art 2).
As described above, in the background art 1 or the background art 2, it is necessary to measure both pulse width and pulse cycle. That is, in order to measure the pulse width, it is necessary to detect both leading and trailing edges of a signal. There is a problem that such edge detection is complicated. Moreover, the detected signal pattern is complex because three kinds of patterns are detected in the background art 1 and four kinds of patterns are detected in the background art 2. Moreover, in order to detect the direction of rotation, it is necessary to calculate signal pulse widths varying continuously as described above and compare the signal pulse widths with one another. There is another problem that detection of the direction of rotation is complicated.
The invention is designed to solve these problems, and an object of the invention is to provide a rotation direction detecting apparatus which can detect the direction of rotation and the rotational velocity of a motor by detecting only leading or trailing edges of a signal.
In order to solve these problems, according to the invention, there is provided a rotation direction detecting apparatus including: a turntable mounted on a rotary shaft of a motor and provided with a predetermined signal pattern, the predetermined signal pattern being formed so that reflection of light and non-reflection of light or transmission of light and non-transmission of light are alternately and continuously repeated by rotation of the motor; a photo-detecting unit for detecting the signal pattern of the turntable; a rotation direction judging unit for judging a direction of rotation of the motor on the basis of the signal pattern detected by the photo-detecting unit; and a velocity calculating unit for calculating a rotational velocity of the motor on the basis of the direction of rotation judged by the rotation direction judging unit, wherein: the signal pattern is set as a pattern in which high-level regions and low-level regions are repeated alternately at a 2:1:1:2 ratio; the rotation direction judging unit judges that the motor is rotating in a direction of normal rotation when leading edges of the signal pattern detected by the photo-detecting unit are arranged at regular intervals, and judges that the motor is rotating in a direction of reverse rotation when leading edges of the signal pattern detected by the photo-detecting unit are arranged at irregular intervals; and the velocity calculating unit calculates the rotational velocity of the motor on the basis of a distance between adjacent leading edges when the rotation direction judging unit judges that the motor is rotating in the direction of normal rotation, and calculates the rotational velocity of the motor on the basis of a distance between two leading edges located on opposite outer sides of three continuous leading edges when the rotation direction judging unit judges that the motor is rotating in the direction of reverse rotation.
According to the invention having such a feature, in a signal pattern which is set as a pattern making repetitions at a 2:1:1:2 ratio, as shown in FIGS. 3A to 3D, the distance between leading edges of the signal pattern at the time of normal rotation of the motor is a constant distance (time interval) t11 (=3t0) whereas the distance between leading edges of the signal pattern at the time of reverse rotation of the motor (that is, the distance between trailing edges of the signal pattern at the time of normal rotation of the motor) alternates between an arrow time interval t12 (=2t0) and a wide time interval t13 (=4t0). Therefore, only leading edges are always detected, so that the rotation direction judging unit judges that the motor is rotating in the direction of normal rotation when the distance between leading edges is a constant time interval t11 (=3t0), and judges that the motor is rotating in the direction of reverse rotation when the distance between leading edges alternates between a narrow time interval t12 (=2t0) and a wide time interval t13 (=4t0). In this manner, the direction of rotation can be detected accurately through simple calculation when only leading edges of the signal pattern are detected.
The velocity calculating unit calculates the rotational velocity of the motor on the basis of the distance t11 (=3t0) between adjacent leading edges when the rotation direction judging unit judges that the motor is rotating in the direction of normal rotation.
The velocity calculating unit also calculates the rotational velocity of the motor on the basis of the distance between two leading edges located on opposite outer sides of three continuous leading edges when the rotation direction judging unit judges that the motor is rotating in the direction of reverse rotation. That is, the rotational velocity of the motor rotating in the direction of reverse rotation cannot be calculated on the basis of only one of the time intervals t12 and t13 because the distance between adjacent leading edges alternates between the narrow time interval t12 (=2t0) and the wide time interval t13 (=4t0). That is, it is impossible to judge whether the given time interval belongs to the narrow one or the wide one. The rotational velocity of the motor rotating in the direction of reverse rotation, however, can be calculated on the basis of the constant time interval t14 (=6t0) because the distance t14 obtained by adding the narrow time interval t12 and the wide time interval t13, that is, the distance t14 between two leading edges located on opposite outer sides of three continuous leading edges is kept constant (2t0+4t0=6t0).
Further, according to the invention, there is provided a rotation direction detecting apparatus including: a turntable mounted on a rotary shaft of a motor and provided with a predetermined signal pattern, the predetermined signal patter being formed so that reflection of light and non-reflection of light or transmission of light and non-transmission of light are alternately and continuously repeated by rotation of the motor; a photo-detecting unit for detecting the signal pattern of the turntable; and a rotation direction judging unit for judging a direction of rotation of the motor on the basis of the signal pattern detected by the photo-detecting unit and constituted by repetition of high- and low-level regions, wherein: the signal pattern is set so that adjacent leading edges of the signal pattern are arranged at regular intervals at the time of normal rotation of the motor whereas adjacent trailing edges of the signal pattern are arranged at intervals each having a value different from that of each of the regular intervals at the time of normal rotation of the motor; and the rotation direction judging unit judges the direction of rotation of the motor on the basis of a judgment as to whether leading edges of the signal pattern detected by the photo-detecting unit are arranged at regular intervals or at irregular intervals. That is, the rotation direction judging unit judges that the motor is rotating in a direction of normal rotation when leading edges of the signal pattern detected by the photo-detecting unit are arranged at regular intervals, and judges that the motor is rotating in a direction of reverse rotation when leading edges of the signal pattern detected by the photo-detecting unit are arranged at irregular intervals.
According to the invention having such a feature, the signal pattern is formed so that the distance between adjacent leading edges at the time of normal rotation of the motor is set to be constant where as the distance between adjacent trailing edges at the time of normal rotation of the motor is set to any desired value different from the former distance. That is, as shown in FIGS. 3A to 3D, the distance between leading edges at the time of normal rotation of the motor is set to be a constant time interval t11 whereas the distance between leading edges at the time of reverse rotation of the motor (that is, the distance between trailing edges at the time of normal rotation of the motor) is set to alternate between a narrow time interval t12 and a wide time interval t13. Therefore, only leading edges are always detected, so that the rotation direction judging unit judges that the motor is rotating in the direction of normal rotation when the distance between leading edges is a constant time interval t11, and judges that the motor is rotating in the direction of reverse rotation when the distance between leading edges alternates between a narrow time interval t12 and a wide time interval t13. In this manner, the direction of rotation can be detected accurately through simple calculation when only leading edges of the signal pattern are detected.
Further, in the rotation direction detecting apparatus according to the invention, the signal pattern is set as a pattern in which high-level regions and low-level regions are repeated alternately at a 2:1:1:2 ratio. As a result, the distance between leading edges at the time of normal rotation of the motor is a constant time interval t11 (=3t0) whereas the distance between leading edges at the time of reverse rotation of the motor (that is, the distance between trailing edges at the time of normal rotation of the motor) alternates between a narrow time interval t12 (=2t0) and a wide time interval t13 (=4t0). Therefore, only leading edges are always detected, so that the rotation direction judging unit judges that the motor is rotating in the direction of normal rotation when the distance between leading edges is a constant time interval t11 (3t0), and judges that the motor is rotating in the direction of reverse rotation when the distance between leading edges alternates a narrow time interval t12 (=2t0) and a wide time interval t13 (=4t0) In this manner, the direction of rotation can be detected accurately through simple calculation when only leading edges of the signal pattern are detected.
Further, according to the invention, the rotation direction detecting apparatus further includes a velocity calculating unit for calculating a rotational velocity of the motor on the basis of a distance between adjacent leading edges when the rotation direction judging unit judges that the motor is rotating in a direction of normal rotation, and for calculating a rotational velocity of the motor on the basis of a distance between two leading edges located on opposite outer sides of three continuous leading edges when the rotation direction judging unit judges that the motor is rotating in a direction of reverse rotation.
According to the invention having such a feature, the direction of rotation can be detected accurately through simple calculation when only leading edges of the signal pattern are detected.